Capacitor discharge ignition system for an internal combustion engine

ABSTRACT

A capacitor discharge electronic ignition circuit for an internal combustion engine is provided with an engine stopping switch that prevents clearing out the charge carriers present in the controlled semiconductor switch of a system when it is conducting, keeping the controlled semiconductor switch turned on and preventing the capacitor from being charged. The turn-on voltage is periodically raised as the engine continues to turn by the control pulses from a tachogenerator and by the positive half waves of the magneto generator output. When a planar thyristor is used as the controlled semiconductor switch, its open circuited control path acts as a capacitor which charges on the timing pulse to hold the planar thyristor in conducting condition until the next positive half wave of the magneto generator comes along to continue the process. By the addition of a capacitor the circuit can be made to operate with other kinds of controlled semiconductor switches as well. The circuit can also be combined with a circuit for assuring that the crankshaft of the engine will not run backwards.

Haubner et al.

[ CAPACITOR DISCHARGE IGNITION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE [75] Inventors: Georg Haubner, Berg; Walter Hofer,

Schwabach; Peter Schmaldienst, Nurnberg, all of Germany [73 Assignee: Robert Bosch G.m.b.H., Stuttgart,

Germany [22] Filed: Feb. 4, 1974 [21] Appl. No.: 439,011

[30] Foreign Application Priority Data Mar. 16, 1973 Germany 2313273 [52] US. Cl. 123/148 CC; 123/148 E [51] Int. Cl. F02? 1/17 [58] Field of Search 123/148 E, 148 CC;

[56] References Cited UNITED STATES PATENTS 3,500,809 3/1970 Hohne et al 123/148 CC 3,791,363 2/1974 Schmaldienst et al. 123/148 CC 3,809,044 5/1974 .lereb et a1 123/148 CC Aug. 19, 1975 Primary Examiner-Wendell E. Burns Assistant Examiner-James Winthrop Cranson, Jr. Attorney, Agent, or F [rm-William R. Woodward [5 7] ABSTRACT A capacitor discharge electronic ignition circuit for an internal combustion engine is provided with an engine stopping switch that prevents clearing out the charge carriers present in the controlled semiconductor switch of a system when it is conducting, keeping the controlled semiconductor switch turned on and preventing the capacitor from being charged. The turn-on voltage is periodically raised as the engine continues to turn by the control pulses from a tachogenerator and by the positive half waves of the magneto generator output. When a planar thyristor is used as the controlled semiconductor switch, its open circuited control path acts as a capacitor which charges on the timing pulse to hold the planar thyristor in conducting condition until the next positive half wave of the magneto generator comes along to continue the process. By the addition of a capacitor the circuit can be made to operate with other kinds of controlled semiconductor switches as well. The circuit can also be combined with a circuit for assuring that the crankshaft of the engine will not run backwards.

13 Claims, 4 Drawing Figures CAPACITOR DISCHARGE IGNITION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE This invention relates to an electronic ignition system of the capacitor-discharge type for an internal combustion engine with an engine stopping switch arranged to prevent the charging of the capacitor.

More particularly the invention relates to ignition systems in which a magneto generator is used to charge a capacitor, and a controlled semiconductor switching element is turned on at the moment of ignition to discharge the capacitor through the primary winding of an ignition transformer to cause a high-voltage pulse to be generated in the secondary winding thereof for producing a spark in a spark plug of the engine.

Known methods of turning off an engine equipped with such an ignition system include the shortcircuiting of the charging winding of the magneto gen erator and, as an alternative, the disconnection of the magneto generator from the charging capacitor, so that in either case the electrical energy necessary for generating an ignition spark will no longer be transferred to the ignition capacitor. Such arrangements require a high-rated sturdy switch, particularly in high-power ignition systems. A switch that short-circuits the charging winding of the magneto generator must be able to carry the short-circuit currents for several seconds without damage. A switch used for disconnecting the charging winding from the capacitor must be able to handle safely voltages from 1 to 2 KV which correspond to the open-circuit voltage of the magneto generator.

In electronically controlled capacitor ignition systems stopping switches are known in which the engine is stopped by short-circuiting a tachogenerator in the control current circuit of the electronic switching element of the system by a relatively small switch, or by interrupting the control current circuit by such a switch. The electronic switching element, which is preferably a semiconductor controlled rectifier, a device also known by the designation SCR and thyristor, loses its control pulses by such a switching operation and is no longer turned on, with the result that the ignition capacitor can no longer be discharged. That has the result that supplementary precautions must be taken to protect the ignition capacitor from overcharging by the magneto generator and to protect the thyristor from overvoltage. I i

It is an object of this invention to provide an electronically controlled capacitor-discharge ignition system with an engine stopping switch so arranged that there is no overloading by voltages greater than the operating voltage or currents greater than the operating current of the engine, either in the ignition circuit or in the stopping switch structure.

SUBJECT MATTER OF THE PRESENT INVENTION closed switch in the control circuit of the semiconductor controlled switch, or it may be a normally open switch that short-circuits the control path of a transistor having its switching path in the control circuit of the semiconductor controlled switch. The open-circuited control path of the semiconductor controlled switch acts like a capacitor that is charged by its remaining connection with the timing tachogenerator in between the positive half waves supplied by the magneto generator which flow through the'semiconductor controlled switch and likewise keep it turned on so long as the stopping switch remains operated.

When a normally closed switch in the thyristor control circuit is used as the stopping control, it is convenient to locate it betweenthe tachogenerator output and ground. It may be provided with a shunt diode grounded on its anode side. A shunt capacitor may be placed across the stopping switch to enable the circuit to be used with a widervariety of thyristors. It may be useful to connect a resistor from the control electrode of the thyristor to the ungrounded side of the magneto generator (i.e. to the anode of the thyristor) tofacilitate keeping the thyristor turned on by the positive half waves of the magneto generator output, this resistor being of such a high value that it has no such effect when the stopping switch is in its rest position andgrounds the tachogenerator winding.

The invention is described by way of examples with reference to the accompanying drawings, in which:

FIG. 1 is a circuit diagram of a capacitor ignition system supplied by a magneto generatorand timed by a tachogenerator provided with a stopping switch circuit according to the invention;

FIG. 2 is a circuit diagram of only the control current circuit of the controlled semiconductor switch of anignition system in other respects like that of FIG. 1;

FIG. 3 is a circuit diagram-of-a different form of control current circuit of the controlled semiconductor;v

switch of an ignition circuit otherwise like that of FIG. I, and i FIG. 4 shows a circuit diagram of part of an ignition circuit showingan enginestopping control combined with the circuit for preventing retrograde operation of theengine, the ignition system being in other respects like that of FIG. 1. i t

FIG. 1 shows the circuit of an ignition system for a one-cylinder internal combustion engine not shown in the drawing. It is supplied by a magneto generator 10 that is composed of a magnet pole wheel 11 driven by the engine and a fixed armature 12 that is provided with a charging current winding 13. One end of thewinding 13 is connected to the anode of a'diode 14',

which has its cathodeconnected to anignition capacitor 15 that is connected inseries with the primary winding 16A of an ignition transformer 16. The'secondary winding 16B of the ignition transformerhas one end.

connected to the primary winding 16A and the other -over an ignition cable 17 to a spark plug 18. The com- 19 constituting the electronic switching element of the system and having a control electrode 19A connected to a tachogenerator 20 driven by the engine. The planar thyristor 19 and the primary winding 16A provide a discharge circuit for the ignition capacitor 15.

The planar thyristor 19 has the property that when a control voltage is applied to its control electrode 19A, charge carriers are introduced into the control path formed by the control electrode and cathode of the thyristor, which charge carriers can be cleared out of this path only over a closed external circuit between the control electrode 19A and the cathode. The control path, therefore, operates as a capacitor and in its charged condition maintains the thyristor conductive. This property is utilized for stopping the engine by keeping the planar thyristor 19 in its conducting condition by interrupting its control current circuit and in this manner preventing the charging of the ignition capacitor 15.

For this purpose a normally closed switch 21 is provided as an engine stopping control in the control current circuit of the thyristor. One side of the switch is grounded to the chassis and the other is connected to the control winding 20A of the tachogenerator with the switch and that winding in series. The control electrode 19A of the planar thyristor 19 is not only connected with the winding 20A but is also connected over a resistor 22 to the positive terminal of the ignition capacitor 15, to which the anode of the thyristor l9 and the cathode of the charging diode 14 are also connected. Since the contacts of the switch 21 are sometimes operated in" the presence of moisture and dirt, in which case no complete interruption of the control current circuit is accomplished, this possible condition is indicated by the leak resistance 23 shown in dashed lines connected in parallel to the switch 21.

' OPERATION or THE CIRCUIT OF FIG. 1

When the engine turns over, the pole wheel 11 is rotated and an alternating current is thereby induced in the charging winding 13. The negative half waves of this alternating current are blocked by the diode 14. The positive half waves pass through the diode 14 and charge the ignition capacitor 15. The charging current circuit is completed over the primary winding 16A of the ignition transformer 16 and over the connection through the chassis ground connecting the ignition transformer 16 and the charging winding 13. According to the particular design of the ignition system the ignition capacitor is charged by one or by two or more positive half waves of the charging current. At the spark timing instantthe tachogenerator 20 produces a positive control pulse that is applied to the control electrode 19A of the planar thyristor 19 and switches the latter into its conducting condition. The ignition capacitor 15 is now suddenly discharged through the discharge circuit composed of the planar thyristor l9 and the primary winding 16A. The powerful change of current thus produced in the primary winding 16A generates a high voltage in the secondary winding 16B of the ignition transformer 16 which in turn produces a spark in the spark plug 18. The engine now runs and the charging and discharging cycles of the ignition capacitor 15 are repeated with every revolution of the pole wheel 11. I

To stop the engine, the switch 21 is opened. The last previous voltage pulse of the tachogenerator 20 is connected to the control electrode 19A put the planar thyristor 19 into its conducting condition. Since the control path of the planar thyristor 19 operates as a capacitor, a voltage is built up over the resistor 22 as the result of the charging of the capacitor 15 that keeps the planar thyristor 19 in its conduction codition. The charge carriers in the control path of the planar thyristor 19 can no longer be cleared out after the switch 21 is opened and the planar thyristor 19 still remains in its conducting condition. The positive half waves arriving from the charging current winding 13 over the diode 14 are henceforth directly conducted to ground over the planar thyristor l9 and consequently no longer reach the ignition capacitor 15. Ignition no longer works and theengine is stopped in this manner.

Since the undefined shunt resistances in the current control circuit of the planar thyristor 19 as well as the variable leak resistance 23 can produce a gradual clearing out of the control path of the planar thyristor 19, it is important that the voltage on the control electrode 19A should be built up again with each revolution of the pole wheel 11 of the magneto generator 10 to such an extent that the planar thyristor 19 is kept conducting at least until the beginning of the next charging half wave of the magneto generator 10. Since the charge carriers in the control path of the planar thyristor 19 are not fully cleared out through the leak resistance 23 when the switch 21 is open, a small additional voltage is sufficient to keep the planar thyristor conducting. This voltage is applied to the control electrode 19A of the planar thyristor 19 as soon as a positive half wave of the magneto generator 10 begins by means of a voltage divider formed by the resistor 22 and the leak resistance 23. In normal operation of the ignition system the resistor 22 has no influence on the control of the planar thyristor 19, because the switch 21 is then closed and the resistor 22 has a very small resistance value in comparison to the resistance of the control winding 20A of the tachogenerator.

FIG. 2 is another illustrative embodiment of an engine stop control in the control current circuit of the planar thyristor 19 of an ignition system, the full charging and discharging circuit of which is apparent by reference to FIG. 1. The control winding 20A of the tachogenerator 20 here again is connected in series with the switch 21. A diode 24 is connected in parallel to the switch 21 with its anode grounded to the chassis.

In'normal operation of the engine the planar thyristor 19 is controlled by a positive control pulse of the tachogenerator to switch into its conducting condition at the ignition timing instant, leading to discharge of the capacitor 15 and the striking of a spark in the spark plug 18. The charge carriers in the control path of the planar thyristor 19 are immediately thereafter cleared out over the current circuit formed by the winding 20A and the switch 21. The switch 21 is opened to stop the engine and thereupon the dissipation of the charge carriers of the control path of the planar thyristor 19 is practically prevented. Since these charge carriers are very gradually cleared out over the shunt resistance 25 of the control path designated in dashed lines, the voltage on the control electrode 19A is built up anew with every revolution of the pole wheel by the positive control pulse of the tachogenerator 20. The diode 24 is so poled that the voltage of this control pulse is applied to it in its direction of easy conduction.

The engine stop circuit of FIG. 2 can be developed in quite a simple way to make it effective also for other thyristors that have a definite resistance in their control paths. In this case a capacitor 26, indicated in dashed lines in FIG. 2 is connected in parallel to the switch 21. When the switch 21 is open, this capacitor 26 is charged by the negative voltage pulses produced by the tachogenerator 20. The discharge of the capacitor 26 thereafter takes place over the control path of the thyristor. During this discharge the thyristor is maintained in its conducting condition until the beginning of a positive half wave of the magneto generator drives a curl ent through the anode-cathode path of the thyristor and thus further keeps the thyristor turned on.

A further illustrative embodiment of the invention is shown in FIG. 3, in which the control Winding A of the tachogenerator 20 is connected over a diode 27 that passes the positive voltage pulses through to the control path of the planar thyristor 19. The switch 21 is in this case connected in series with a resistor 28 and this series combination is connected between the control electrode 19A and the cathode of the planar thyristor 19. y

In normal operation of the engine the planar thyristor 19 is switched into its conducting condition at the spark timing instant by a positive voltage pulse of the tachogenerator 20. The charge carriers in the control path of the planar thyristor 19 are then immediately carried away over the resistor 28 and the switch 21. The diode 27 prevents the charge carriers from flowing away over the control winding 20A. To stop the engine the switch 21 is opened, thereby interfering with the clearing out of the charge carriers in the control path of the planar thyristor 19. The switching path of the planar thyristor 19 accordingly remains in its conducting condition and effectively bridges the charging winding of the magneto generator, shown in FIG. 1, during its positive half waves.

The illustrative embodiment shown in FIG. 4 has an engine stopping device in the control current circuit of a capacitor ignition system which is combined with a circuit for preventing reverse operation of the crankshaft of the engine. The charging winding 13 of the magneto generator 10 shown in FIG. 1 is to be regarded as connected at the input of the circuit of FIG. 4. Likewise, the ignition capacitor 15 and the ignition transformer l6 and its circuit for the spark plug 18, as shown in FIG. 1, are to be regarded as connected in parallel to the switching path of the normal thyristor 19B shown in FIG. 4. The input of the ignition system is connected over a diode 30 to a voltage divider composed of two series connected resistors 31 and 32. The tap of the voltage divider is connected to the base of an npn transistor 33. The emitter of the transistor 33 is grounded to the chassis and its collector is connected over another diode 34 with the control electrode 19C of the thyristor 198. The control winding 20A of the tachogenerator 20 has one end grounded to the chassis and the other end connected over still another diode 35 with the collector of the transistor 33.

The engine stopping device is constituted in this case by the transistor 33, which has its switching path grounded to the chassis on one side and connected on the other side over a resistor 36 and the diode 30 with the ungrounded terminal of the magneto generator 10 and has its control path arranged so it can be bridged by closing a normally open switch 37.

In normal operation of the engine the positive half waves of the magneto generator reach the ignition capacitor 15 over the diodes 30 and 14 and charge it. The resulting voltage drop produced across the resistor 32 of the voltage divider switches the transistor 33 into its conducting condition and thereby grounds one end of the resistor 36. The negative half waves of the magneto generator 10 are blocked by the diode 30. The resistors 31 and 32 then carry no current and the transistor 33 is again blocked. The voltage pulse produced by the control winding 20A of the tachogenerator 20 at the ignition timing instant reaches the control electrode 19C of the thyristor 198 over the diodes 35 and 34 during the negative half wave of the magneto generator and initiates ignition. Rotation in the wrong direction, however, induces a positive half wave in the charging winding of the magneto generator at the time of a spark timing pulse, and the positive half wave switches the transistor 33 into its conducting condition over the resistors 31 and 32, so that the positive voltage pulses of the tachogenerator 20 are in this way drawn off to ground. In consequence, turning on of the thyristor 19B is prevented.

To turn off the engine the switch 37 is closed, thus bridging the control path of the transistor 33. The switching path of the transistor 33 therefore remains blocked and when the positive half wave of the magneto generator begins, it is passed on over the resistor 36 and the diode 34 to the control electrode 19C of the thyristor 19B and switches the latter into its conducting condition. In this manner the magneto generator I0 is short circuited by the thyristor 198, thus preventing the charging up of the ignition capacitor 15 that is necessary to produce ignition.

The invention is not limited to the examples of circuits and components shown in the drawings, since, for example, instead of the planar thyristor 19 there may also be used four layer diodes or other semiconductor elements. What is important for the invention is that a charging up of the ignition capacitor by a timely switching of the electronic switching element into its blocking condition is prevented by the actuation of the engine stopping device.

We claim:

1. Electronically controlled ignition system of the capacitor-discharge type for an internal combustion engine, comprising, in combination with a magneto generator (10), an ignition transformer (16) having low and high voltage windings, spark-timing pulse generator means (20), at least one spark plug (18) in circuit with said high-voltage winding, and control circuit means including the following:

a capacitor (15) and a controlled semiconductor switch (19) arranged in circuit, so that said capacitor may be charged by said magneto generator (10) and discharged through said semiconductor switch (19) and said low-voltage winding (16A) of said transformer, said controlled semiconductor switch having a control electrode, and

ignition disabling means (21) in circuit both with said spark-timing pulse generator and with the control electrode of said controlled semiconductor switch, so connected as to produce, when said disabling means is put into disabling position, a voltage on said control electrode that, by the time the next charging halfwave of said magneto generator begins, at the latest, causes said controlled semiconductor switch to short-circuit the discharge circuit of said capacitor 2. Ignition system as defined in claim 1 in which said control electrode (19A) is arranged to have the voltage thereon increased by output pulses provided by said spark-timing pulse generator (20), and said disabling means (21) is arranged so that when it is put into disabling position, the voltage so built up on said control electrode is approximately fully stored at least until the beginning of the next charging half-wave produced by said magneto generator (10).

3. Ignition system as defined in claim 2 in which said disabling means comprises switching means with normally closed switching contacts in circuit in the control current circuit of said controlled semiconductor switch (19).

4. Ignition system as defined in claim 3 in which said switching means (21) constituting said disabling means has one of its contacts connected to chassis ground.

5. Ignition system as defined in claim 3 in which said spark-timing pulse generator (20) is an electromagnetic tachogenerator having an output winding (20A) and in which, further, said switching means (21) constituting said disabling means is connected in series with said output winding (28) of said tachogenerator.

6. Ignition system as defined in claim 5 in which one of said contacts of said switching means (21) of said disabling means is connected to chassis ground and in which diode means (24) are connected in parallel to said switching means the anode side of said diode means connected to chassis ground.

7. Ignition system as defined in claim 4 in which a resistance (28) is connected in series with said switching means, and the series combination of said switching means and said resistance is connected between the control electrode (19A) and the cathode of said controlled semiconductor switch and in which means (27) are provided for blocking charge carrier clearing of said controlled semiconductor switch otherwise than through said resistance 28).

8. Ignition system as defined in claim 6 in which a second capacitor (26) is connected in parallel to said switching means 21) of said disabling means.

9. Ignition system as defined in claim 3 in which a resistance (22) is connected between said control electrode (19A) of said controlled semiconductor switch (19) and the positive terminal of said capacitor (15).

10. Ignition system as defined in claim 3 in which said magneto generator 10) has a grounded output terminal and an ungrounded output terminal, and in which a resistance (22) is connected between said control electrode 7 (19A) of said controlled semicondutor switch and, over a diode, to said ungrounded terminal of said magneto generator.

l 1. Ignition system as defined in claim 1 in which the charging half-wave of said magneto generator (10) is caused, by operation of said disabling means (21), to apply voltage to said control electrode (19C) of said controlled semiconductor switch (19B).

12. Ignition system as defined in claim 11 in which said magneto generator has one grounded output terminal and one ungrounded output terminal and in which said disabling means includes a transistor (33) one end of the switching path of which is connected to chassis ground and the other, over a resistance (36), to said ungrounded terminal of said magneto generator (10) and in which normally open switch means (37) are provided for short-circuiting the control path of said transistor (3) and thereby operating said disabling means. i

13. Ignition system as defined in claim 1 in which said controlled semiconductor switch is a planar thyristor. l 

1. Electronically controlled ignition system of the capacitordischarge type for an internal combustion engine, comprising, in combination with a magneto generator (10), an ignition transformer (16) having low and high voltage windings, sparktiming pulse generator means (20), at least one spark plug (18) in circuit with said high-voltage winding, and control circuit means including the following: a capacitor (15) and a controlled semiconductor switch (19) arranged in circuit, so that said capacitor may be charged by said magneto generator (10) and discharged through said semiconductor switch (19) and said low-voltage winding (16A) of said transformer, said controlled semiconductor switch having a control electrode, and ignition disabling means (21) in circuit both with said sparktiming pulse generator and with the control electrode of said controlled semiconductor switch, so connected as to produce, when said disabling means is put into disabling position, a voltage on said control electrode that, by the time the next charging halfwave of said magneto generator begins, at the latest, causes said controlled semiconductor switch to shortcircuit the discharge circuit of said capacitor (15).
 2. Ignition system as defined in claim 1 in which said control electrode (19A) is arranged to have the voltage thereon increased by output pulses provided by said spark-timing pulse generator (20), and said disabling means (21) is arranged so that when it is put into disabling position, the voltage so built up on said control electrode is approximately fully stored at least until the beginning of the next charging half-wave produced by said magneto generator (10).
 3. Ignition system as defined in claim 2 in which said disabling means comprises switching means with normally closed switching contacts in circuit in the control current circuit of said controlled semiconductor switch (19).
 4. Ignition system as defined in claim 3 in which said switching means (21) constituting said disabling means has one of its contacts connected to chassis ground.
 5. Ignition system as defined in claim 3 in which said spark-timing pulse generator (20) is an electromagnetic tachogenerator having an output winding (20A) and in which, further, said switching means (21) constituting said disabling means is connected in series with said output winding (28) of said tachogenerator.
 6. Ignition system as defined in claim 5 in which one of said contacts of said switching means (21) of said disabling means is connected to chassis ground and iN which diode means (24) are connected in parallel to said switching means the anode side of said diode means connected to chassis ground.
 7. Ignition system as defined in claim 4 in which a resistance (28) is connected in series with said switching means, and the series combination of said switching means and said resistance is connected between the control electrode (19A) and the cathode of said controlled semiconductor switch and in which means (27) are provided for blocking charge carrier clearing of said controlled semiconductor switch otherwise than through said resistance (28).
 8. Ignition system as defined in claim 6 in which a second capacitor (26) is connected in parallel to said switching means (21) of said disabling means.
 9. Ignition system as defined in claim 3 in which a resistance (22) is connected between said control electrode (19A) of said controlled semiconductor switch (19) and the positive terminal of said capacitor (15).
 10. Ignition system as defined in claim 3 in which said magneto generator (10) has a grounded output terminal and an ungrounded output terminal, and in which a resistance (22) is connected between said control electrode (19A) of said controlled semicondutor switch and, over a diode, to said ungrounded terminal of said magneto generator.
 11. Ignition system as defined in claim 1 in which the charging half-wave of said magneto generator (10) is caused, by operation of said disabling means (21), to apply voltage to said control electrode (19C) of said controlled semiconductor switch (19B).
 12. Ignition system as defined in claim 11 in which said magneto generator has one grounded output terminal and one ungrounded output terminal and in which said disabling means includes a transistor (33) one end of the switching path of which is connected to chassis ground and the other, over a resistance (36), to said ungrounded terminal of said magneto generator (10) and in which normally open switch means (37) are provided for short-circuiting the control path of said transistor (3) and thereby operating said disabling means.
 13. Ignition system as defined in claim 1 in which said controlled semiconductor switch is a planar thyristor. 